Ironically large doses of vitamin C have been PROVEN to be bad for T2 diabetes. Almost all of the insulin absorption benefits of exercise get wiped out with mega doses of Vit C.
As for mommy, dont argue, dont over share, just say "Oh, that's interesting" or " I'll have to think about that" "Oh, you know, I HAVE heard that before" (you dont have to say FROM YOU) and change the subject. Try to avoid talking to her about anything your doctor says. Talk about innocuous subjects.